In recent years, as disc rotation speeds have increased during the reading of data in optical disc drives typified by a CD-R drive and a DVD-R drive and data have been written to an optical disc, there has been a demand for photoelectric conversion ICs which can correctly amplify both of a high-frequency signal during the reading of data and a pulsed signal during the writing of data. Further, photoelectric conversion ICs which can accommodate different standards of optical discs are demanded.
Such photoelectric conversion ICs can be achieved by switching frequency characteristics and gains (amplification factors) in current-voltage converters which convert current from photo diodes to voltage.
FIG. 18 is a diagram showing an example of a current-voltage converter included in a conventional photoelectric conversion IC.
The current-voltage converter comprises an amplifier APi for converting a current signal from a photo diode PDi to a voltage signal, a feedback capacitor Cf and a feedback resistor Rf of the amplifier APi, and an analog switch circuit (junction FET) 14 for switching the gains and feedback capacitances of the amplifier APi.
The cathode of the photo diode PDi connects to the inverting input terminal of the amplifier APi. Meanwhile, the anode of the photo diode PDi is grounded. The inverting input terminal of the amplifier APi receives a light-receiving current signal from the photo diode PDi and the noninverting input terminal of the amplifier APi is fed with intermediate voltage Vs (½ Vcc) of reference voltage Vcc.
The amplifier APi comprises a differential amplifier circuit 11 for current-voltage conversion which converts the light-receiving current signal from the photo diode PDi to a voltage signal, a phase compensation section 12 for performing selected phase compensation on a signal from the differential amplifier circuit 11, and an output circuit 13 for amplifying, in a push-pull manner, a signal whose phase has been compensated by the phase compensation section 12. The phase compensation section 12 includes an analog switch circuit (junction FET) 14. The analog switch circuit 14 is turned on/off in response to a control signal Vm. In response to the on/off of the analog switch circuit 14, the gain of the amplifier APi is switched, and simultaneously the feedback capacitance of the amplifier API and the resistance value and the capacitance value of the phase compensation section are also switched.
In this way, the current-voltage converter makes it possible to adjust the frequency characteristics of the amplifier APi.
The conventional photoelectric conversion IC including the current-voltage converter configured thus is able to change the gain of the amplifier APi so as to obtain a constant output voltage, even when the power of light (amount of reflected light) reflected from an optical disc and incident on the photo diode PDi is varied among the different standards of optical discs or due to whether data are written or read. Further, the conventional photoelectric conversion IC is able to adjust frequency characteristics depending on the different standards of optical discs and the state of writing or reading by changing the feedback capacitance of the amplifier APi and the resistance value and capacitance value of the phase compensation section (For example, Japanese Patent Laid-Open No. 10-107563).